Quick T-SQL Tip #2: Identity Columns Seed Value

This post really deals with high volume tables with an identity column, but the idea is something that everyone should at least be familiar with.

Quite often I see table creation scripts that start like this:

Create Table ATable
(
ID int not null identity(1,1)
...

And while that is perfectly legal and will work with no issues, if this table is going to be a high volume table, you should consider using the entire Int, not just half of one.

What??

The Int data type spans -2,147,483,648 thru 2,147,483,647.  If your seed is 1, you lose 2,147,483,649 values that could be used.

I have seen production situations where they have run out of identity values because the seed was 1.
So, next time you create an Identity, ask yourself: "Two billion, or four billion?"

and then 

Create Table ATable
(
ID int not null identity(-2147483648,1)
...

peace

DateTime Columns in Slowly Changing Dimension Component

We had an interesting error when implementing a slowly changing dimension in SSIS this week.

We had a date column that we were passing thru to the database from the source. However, the source was a script task because it came in from a multi-resultset stored procedure. In other data flows, where we were using an OLE DB destination, we typed datetime columns as DT_DATE. However, when we used DT_DATE with the slowly changing dimension component, it threw an error:

Error at Import Data [Slowly Changing Dimension]:The input column "input column "ALDATE (15157)" cannot be mapped to external column "external column "ALDATE (15160)" because they have different data types. The Slowly Changing Dimension transformation does not allow mapping between column of different types except for DT_STR and DT_WDTR.

After much digging and research, we determined that we had to set the output column type on the script component to DT_DBTIMESTAMP. Once we changed that, the SCD worked just fine!

peace